Faulty or drifting engine coolant temperature sensor; Faulty or drifting engine oil temperature sensor, where fitted; Wiring or connector fault on either sensor circuit, such as corrosion, chafing or high resistance; Thermostat stuck open or slow to open, so coolant temperature does not rise normally; Low coolant level or air trapped in the cooling system giving false coolant readings; Oil cooler or coolant-to-oil heat exchanger fault affecting oil temperature rise, which depends on the engine; Engine control unit fault or outdated calibration, where the manufacturer has identified one.

P012F

Engine Coolant Temperature / Engine Oil Temperature Correlation.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
2F: FaultThe specific fault in that area

What it means

P012F means the engine control unit has compared the engine coolant temperature and engine oil temperature readings and found they do not agree as expected. After a cold soak the two should read close to each other, and during warm-up they should rise in a believable relationship. The code sets when the difference is outside the calibrated limit or one reading fails to follow the other.

Symptoms

Engine warning light on
Temperature gauge reading oddly, or slow to reach normal operating temperature
Cooling fans running at unexpected times
Poor fuel economy or rough running while warming up
Heater output weaker than normal
Hard starting when cold or hot, depending on which reading is wrong

Possible causes

Faulty or drifting engine coolant temperature sensorlikely
Faulty or drifting engine oil temperature sensor, where fittedlikely
Wiring or connector fault on either sensor circuit, such as corrosion, chafing or high resistancepossible
Thermostat stuck open or slow to open, so coolant temperature does not rise normallypossible
Low coolant level or air trapped in the cooling system giving false coolant readingspossible
Oil cooler or coolant-to-oil heat exchanger fault affecting oil temperature rise, which depends on the enginerare
Engine control unit fault or outdated calibration, where the manufacturer has identified onerare

How to diagnose

Read and record the freeze frame data and check for any other stored codes, especially coolant, oil temperature or sensor circuit codes
Check coolant level and oil level, and look for leaks or signs of overheating
Inspect both sensor connectors and wiring for damage, corrosion, water ingress and poor pin tension
After the engine has cold soaked for several hours, compare live coolant and oil temperature readings with each other and with ambient temperature
Watch both readings during warm-up and note which one is implausible, stuck or rising too slowly
Check the thermostat is opening at the right temperature by observing coolant temperature behaviour and hose warmth
Test each sensor resistance and circuit voltage against the manufacturer specification for that engine
Check for manufacturer service information on calibration updates or known faults for the model, as the oil temperature setup varies by engine

How to fix

Replace the sensor that has been proven faulty, whether coolant or oil temperature
Repair or replace damaged wiring and clean or renew faulty connectors
Replace a thermostat that is stuck open or opening late
Top up and correctly bleed the cooling system, and repair any leak found
Repair or replace a faulty oil cooler or heat exchanger as per the manufacturer procedure
Update the engine control unit calibration only if an outdated or faulty calibration is a documented cause

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but get it checked soon because a wrong temperature reading can affect fuelling and fan control. Stop and investigate straight away if the temperature gauge rises abnormally, the coolant level is low or there are signs of overheating.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.